1. Field of the Invention
The present invention relates to a liquid ejection apparatus and an ejection control method, and more particularly, to an ejection control technology for a liquid ejection apparatus which forms shapes such as images or prescribed patterns on an ejection receiving medium, by ejecting liquid droplets from ejection holes.
2. Description of the Related Art
In recent years, inkjet printers have come to be used widely as data output apparatuses for outputting images, documents, or the like. By driving recording elements, such as nozzles, provided in a recording head in accordance with data, an inkjet printer is able to form data onto a recording medium, such as recording paper, by means of ink ejected from the nozzles.
In an inkjet printer, a desired image is formed on a recording medium by causing a recording head having a plurality of nozzles and a recording medium to move relative to each other, while causing ink droplets to be ejected from the nozzles.
Until now, inkjet printers have been using as apparatuses for outputting documents principally in domestic and office scenarios, but recently, they have started to be used for outputting images captured by digital cameras, and the like. Furthermore, there are also inkjet apparatuses which are compatible with A3 and poster size recording media, and hence they have come to be used for outputting publicity prints, posters, or the like.
Good image resolution is an important requirement in image printing, and high-quality image printing is achieved by developments such as multi-color printing, multiple tone graduation, finer dot size, higher dot density, and the like. For example, by using multiple ink colors, such as light color inks, it is possible to achieve full color and multiple-stage tone graduation. By increasing the density of the nozzle arrangement and reducing the droplet size, it is possible to increase dot density and reduce dot size in the image. Moreover, if droplet ejection control is performed in order that ink is ejected in such a manner that adjacent dots are mutually overlapping, then the dots can be formed to a high density on the recording medium.
However, when adjacent dots are formed in an overlapping fashion, if the subsequent ink droplet is deposited before the previously deposited ink has become fixed in the recording medium, then the shape of the respective dots is disrupted, the subsequently deposited ink droplet moves towards the previously deposited ink droplet, and streaking or non-uniformity may occur in the resulting image. Furthermore, if inks of different colors are deposited in an overlapping fashion, then color mixing occurs, and it becomes impossible to achieve the desired colors and tone graduation.
In general, various methods are used in order to prevent deposition interference between dots of this kind. For example, droplet ejection control is implemented in order that a subsequent ink droplet is ejected after waiting for a previously deposited ink droplet to permeate to a certain degree into the medium. Alternatively, a temperature adjusting device is provided which warms the recording medium onto which ink has been deposited and the ink that has been deposited on the recording medium, and the fixing of the ink is accelerated by using of this temperature adjusting device. In a further method, an ultraviolet curable ink is used to form the image, and fixing of the ink deposited on the recording medium is accelerated by irradiating ultraviolet light onto the ejected ink.
Japanese Patent Application Publication No. 6-183129 discloses an inkjet recording method and an inkjet recording apparatus using this method, in which recording is performed by moving a plurality of recording heads disposed in a parallel arrangement with respect to a recording medium, the method being composed in such a manner that recording timings are staggered between recording of either one of the ink dots contacting a border between ink dots of different inks, and recording of other ink dots.
Japanese Patent Application Publication No. 2002-120361 discloses an inkjet recording apparatus comprising a drum for fixing paper in position and a plurality of inkjet heads disposed facing the drum at prescribed intervals apart in the circumferential direction of the drum, color printing being performed onto the paper by driving the inkjet heads while rotating the drum. The inkjet recording apparatus is composed in such a manner that time T until dots of different colors make contact or overlap mutually at their deposition point on the paper is T≧10 msec.
Japanese Patent Application Publication No. 2000-177115 discloses a printing method and a print head apparatus using this method, in which an electrostatically charged ink is used, and a channel for ejecting ink is provided between electrodes which generate an electrical field. The electrical field acts on the ink ejected from the channel and thus deflects the direction of ejection of the ink.
Japanese Patent Application Publication No. 2000-185403 discloses an inkjet nozzle, inkjet recording head, inkjet cartridge and inkjet recording apparatus, in which a plurality of heaters that generate air bubbles in the ink are provided at the nozzles. By controlling the heaters, different types of bubbles are generated in the ink and hence the direction of flight of the ink can be deflected.
However, if a subsequent ink droplet is ejected after waiting until a previously deposited ink droplet has permeated to a certain degree, then it is necessary to provide a time differential between the landing times of adjacently positioned dots, and this places a restriction on high-speed printing. Furthermore, if fixing of the ink is accelerated by means of heat or ultraviolet light, then it is necessary to provide a temperature adjustment device or ultraviolet light source, in addition to which, the type of ink and the type of media that can be used may be limited.
In the inkjet recording method and the inkjet recording apparatus using same described in Japanese Patent Application Publication No. 6-183129, and the inkjet recording apparatus described in Japanese Patent Application Publication No. 2002-120361, high image quality is achieved by preventing bleeding or reduced concentration through specifying the deposition timings between inks of different colors, but neither the issue of deposition interference between ink droplets of the same color, nor the issue of high-speed printing, are resolved.
Furthermore, in the printing method and the print head device using same described in Japanese Patent Application Publication No. 2000-177115, and the inkjet nozzle, inkjet recording head, inkjet cartridge, and inkjet recording apparatus described in Japanese Patent Application Publication No. 2000-185403, a method is disclosed which prevents image degradation such as non-uniformity, by deflecting the direction of flight of the ejected ink droplets, but no disclosure is provided with regard to a control method for preventing deposition interference or issues relating to same.